Rotary printing machines, for example offset printing machines, frequently supply paper webs to a folding apparatus. The respective multiple paper webs are supplied to the folder by a structure including a plurality of turning bars or the like, and run-in or supply rollers which then feed the paper webs to a combining region, usually a combining plane, for subsequent handling in the folding apparatus (see, for example, German Patent Disclosure Document DE-OS NO. 24 35 583). It is possible that the web may tear as it is being fed to the folding device within the apparatus. It is then necessary to manually thread the respectively torn web through the entire structure. Known web threading devices are only suitable for threading torn paper webs through the printing stations and the dryer, but not through the folding structure itself--see, for example, German Patent DE-PS No. 22 41 127. Manual threading through such a folding apparatus is difficult.